everytime I decide to spend some time with D I have to setup the whole envoirement from scratch, because so much time has passed by.
And everytime I spend so much time to figure out how it works. Descent is a really good eclipse-plugin for D, but it is so damn confusing to me, how everything works. And everytime I get errors like "dmd is not in $PATH" or "Variable references empty selection: ${project_loc}". That is so frustrating.

This time I took a closer look at the dsss-project and I was really impressed by the ease of setting d-compilers up and running. It is not a great effort compiling a larger project with this tool. But I have the lack of IDE integration and to this very moment I couldn't figure out how to set things up with descent. (Btw. I want to use tango. DSSS is configured to use tango.)

Is there a easy and fast way of connecting these two worlds together? Tomorrow work starts over and I will have litte time for D again.

Just speculating here...
AFAIK, the only support Descent has for building is that it can configure external tools. To use DSSS as an external tool, you could either set up a tool that calls rebuild on a certain file, or you could write a dsss.conf (they're very easy) that builds your project and just call dsss.

0. Change Name to "DSSS"
1. Change Location to point to dsss
2. Change Arguments to "build"
3. Create a dsss.conf file in every project you want to be able to build with dsss
4. Now when you run the external tool it will compile the active project (Run -> External Tools -> DSSS)
5. Right click on the executable in Project Explorer and choose run Run As -> D Application

I've installed DSSS with phobos. DSSS has no problem finding this lib. Descent however marks every keyword red. I've included the phobos lib into "build path" as user library. Descent has no problems finding modules like stdio after the point-operator for autocompletion, but "std" is still marked red. Why is that so?

I would guess it's marked orange because the spell check is enabled by default. Window -> Preferences -> General -> Editors -> Text Editors -> Spelling -> uncheck "Enable spell check". If it's really an error than an icon (a read cricle with a cross) will appear in the right edge of the text editor and also a read marking in the left edge.

I've found a strange behavior while using dsss (a very smart thing BTW.) with descent: After updating to the latest Windows 7 Version (I am an early adopter! *g*) I restructured my programming-directory. Therefor I moved DSSS, my D projects, etc. a little bit around on my hard drive, installed eclipse (descent works fine with eclipse x64 version BTW.) and reconfigured my external tool-set to fit the new directories.

But now the strangeness: While compiling a project with dsss I get a console-message saying "Error: dmd is not in $PATH"

Okay... DMD is in $PATH, also DSSS is.

And: The project compiles successfully! Both in CMD and in Eclipse-Descent!